v3.26.1
REGULATORY MATTERS (Regulatory Liabilities) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 542,000 $ 563,000
Less Current Portion 130,114 143,851
Total Noncurrent Regulatory Liabilities 412,250 419,132
Income Taxes Payable through Future Rates    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 198,000 199,000
Renewable Energy Standard    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 103,000 102,000
Deferred Investment Tax Credits    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 102,000 94,000
Net Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 68,000 75,000
Pension and Other Postretirement Benefits (Note 7)    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 32,000 32,000
Over-Recovered Fuel and Purchased Energy Costs    
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 16,000 32,000
Derivatives (Note 8)    
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 4 years  
Total Regulatory Liabilities $ 14,000 20,000
Demand Side Management    
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 9,000 $ 9,000